Layering is the key for cold weather riding. I've ridden in very cold and not so cold. When it is not too cold, I will wear summer weight knee warmers, and arm warmers and maybe a very light (wind breaker, can be folded up in a pocket) type of Jacket.

The next step is to change the leg warmers to full length tights, and add some summer weight wool socks, like smartwool lightweight socks, and maybe a lightweight long sleeve by itself of under a short sleeve jersey.

As it gets colder, I wear thermafleece tights (umm warm and toasty), a polyproplyene undershirt, under short sleeve or warmer long sleeve jersey (toasty, thick one), and a little heavier jacket. The jackets can cause you to sweat so often times I start out with them but take it off as I warm up and before I get too sweaty. You can wear a light weight long fingered glove, specialized makes a pretty good one.

Then, you add the toe covers, then booties, and thick wool socks (like wooly boolies) under your shoes with all the booties and toe covers on top. At about this time, you add a ear warmer over your ears. Sometimes a balaclava to cut out the cold air from the airways so you can breath especially if you have asthma. Good gloves that is the hardest thing to find - try some wind proof ones.

Now, the next step is the really hardcore, pearlizumi (i forgot what they call them, they are thermafleece with a wind protection layer on the front, a really good say GORE jacket for really cold riding! (When it gets this cold, I usually don't ride - it just isn't worth it for me) BUT it can be done! All this with the other stuff underneath.

Now, the trick is how to figure out how to budget all of this when you don't have any of it!